bromate ion measurement method and apparatus

ABSTRACT

A method for measuring bromate ion is provided that provides high-sensitivity measurement results more simply and more quickly than conventional bromate ion measurement methods. A fluorescent substance that is quenched by coexistence with bromate ions is added to a sample and the fluorescence intensity of the fluorescent substance after quenching is measured, the measured fluorescence intensity being subtracted from the fluorescence intensity of a standard sample containing no bromate ions to calculated the fluorescence intensity difference. The bromate ion concentration is calculated from the calculated fluorescence intensity difference, using a pre-determined calibration line between the fluorescence intensity difference and the bromate ion concentration.

TECHNICAL FIELD

The present invention relates to a method and to an apparatus formeasurement of bromate ions in water. More specifically, the presentinvention relates to a method and to an apparatus that can simply,quickly, and with high accuracy, measure minute amounts of bromate ionsgenerated by ozone treatment in high standards purification of water.

BACKGROUND ART

Water sources, such as river water, contain minute amounts of bromineions, and when ozone treatment (water purification treatment to highstandards) is performed, the bromate ions in the water react with ozone,and a reaction such as shown in FIG. 1 occurs, thereby generatingbromate ions.

Bromate ions are considered to be carcinogenic and having genotoxicity,the WHO (World Health Organization) has set guideline values for theconcentration thereof in drinking water at 0.01 mg/L, and in Japan aswell, as of May 30, 2003, an amendment by ministry order was effectedthat sets the water quality standard value at 0.01 mg/L.

An analytical method generally used for analyzing bromate ions is theion chromatograph post-column absorption intensity method. Thisanalytical method is one in which bromate ions in a water sample areseparated using a cation exchange column, sulfuric acid and an admixtureof sodium nitrate and potassium bromide being added to the solution toconvert the bromate ions into tribromine ions, and the tribromine ionmethod being used to measure the ultraviolet region absorption so as toperform quantitative determination. After the bromate ions are separatedusing chromatographic separation, the post column derivitization methodby means of the tribromine ion method is used to measure the level ofabsorption of the 268 nm ultraviolet line.

In the ion chromatograph post-column (IC-PC) method, a two-stagereaction occurs: in the first reaction stage, bromate is converted by apotassium bromide/sulfuric acid solution to tribromine ions, and then inthe second reaction, a sodium bromide solution is used to establish thelinearity of the calibration line in the low-concentration region.

BrO₃ ⁻+5Br⁻+6H⁺→3Br₂+3H₂O

Br₂+Br⁻→Br₃ ⁻

In the past, the color comparison method, the absorption intensitymethod, the gas chromatography method, and the ion chromatography methodand the like have been used as methods for measuring bromate ions. Withthese methods, however, there were problems regarding sensitivity andinterference by coexisting components, and it was difficult to makereliable determinations of bromate ions not exceeding 0.01 mg/L. Incontrast, in Patent Reference 1, there is language describing art bywhich a reducing agent is added to a reagent, the reagent to which thereducing agent was added being used to determine minute quantities ofions in the liquid under measurement. Also, in Non-Patent Reference 1,there is language describing an absorption intensity method that uses a1-cm cell, and in Non-Patent Reference 2, there is language describingan absorption intensity method that uses a 10-cm cell.

PRIOR ART REFERENCES

-   Patent Reference 1: Japanese Patent Application Publication No.    9-119925.-   Non-Patent Reference 1: A. Afkhami, T. Madrakian, M. Bahram, J.    Hazard. Master, B123. 250-255 (2005).-   Non-Patent Reference 2: S. Farrell et al, Anal. Chim Acta, 313,    121-129 (1995).

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

With the methods of measuring bromate ions of the past, there wereproblems of a complex apparatus configuration and the need for a largeamount of time for the derivitization to tribromine ions.

Given the above, the present invention has as an object to provide amethod and an apparatus for bromate ion measurement that can morequickly and simply perform and obtain higher-sensitivity measurementresults than with conventional bromate ion measurement methods.

Means for Solving the Problem

To achieve the above-noted object, the method for measuring bromate ionsaccording to the present invention includes a step of mixing afluorescent substance that is quenched by coexistence with bromate ionsunder acidic conditions with a sample; a step of measuring theflorescence intensity after the quenching of the fluorescent substance;a step of subtracting the measured fluorescence intensity from thefluorescence intensity of a standard sample that does not containbromate ions to calculate the fluorescence intensity difference; a stepof using a pre-determined calibration line between the fluorescenceintensity difference and the bromate ion concentration to calculate thebromate ion concentration from the calculated fluorescence intensitydifference; and a step of determining the bromate ion concentration inthe sample by measuring the fluorescence intensity after quenching ofthe fluorescent substance.

The method for measuring the bromate ions according to the presentinvention may have a step of adding a chelating agent to the samplebefore the step of mixing the fluorescent substance and the sample. Thefluorescent substance used in the method of measuring bromate ionsaccording to the present invention is most preferably trifluoroperazine,and the chelating agent used in the method for measuring bromate ionsaccording to the present invention may be ethylene diamine tetraacetate.

Additionally, another embodiment of the present invention is anapparatus for measuring the bromate ions included in a sample,comprising means for mixing a fluorescent substance that is quenched bycoexistence with bromate ions under acidic conditions with the sample;means for measuring the fluorescence intensity after the quenching ofthe fluorescent substance; means for subtracting the measuredfluorescence intensity from the fluorescence intensity of a standardsample that does not contain bromate ions to calculate the fluorescenceintensity difference; and means for using a pre-determined calibrationline between the fluorescence intensity difference and the bromate ionconcentration to calculate the bromate ion concentration from thecalculated fluorescence intensity.

The apparatus for measuring bromate ions according to the presentinvention may be constituted so as to measure with the fluorescenceintensity measuring means the admixture of the sample and thefluorescent substance that is temporarily held in the mixing means.

The apparatus for measuring bromate ions according to the presentinvention may be constituted so as to measure with the fluorescenceintensity measuring means the admixture of the sample and thefluorescent substance that flows continuously in the mixing means.

EFFECT OF THE INVENTION

As described in detail below, the method for measuring bromate ionsaccording to the present invention can simply and quickly providehigh-sensitivity bromate ion concentration measurement results. Also, byadding a chelating agent as a metallic ion masking agent, it is possibleto obtain high-sensitivity bromate ion concentration measurementresults, regardless of a metallic ion included in the sample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 Drawing showing the mechanism of generation of bromate ions byozonification.

FIG. 2 Graph showing the fluorescent spectrum for different bromate ionconcentrations.

FIG. 3 Graph showing the relationship between the addedtrifluoroperazine concentration and the fluorescence intensitydifference.

FIG. 4 Graph showing the results of measuring the bromate ionconcentration when hydrochloric acid is used as the acid solution.

FIG. 5 Graph showing the results of measuring the bromate ionconcentration when nitric acid is used as the acid solution.

FIG. 6 Graph showing the results of measuring the bromate ionconcentration when sulfuric acid is used as the acid solution.

FIG. 7 Graph showing the results of measuring the relationship betweenthe hydrochloric acid concentration and the fluorescence intensity whenhydrochloric acid is used as the acid solution.

FIG. 8 Graph showing the relationship between the reaction time anddifferent bromate ion concentrations.

FIG. 9 Graph showing the relationship (calibration line) between thebromate ion concentration and the fluorescence intensity difference.

FIG. 10 Simplified schematic representation of an apparatus having abatch-type configuration for the purpose of performing measurement ofbromate ions according to the present invention.

FIG. 11 Simplified schematic representation of an apparatus having aflow injection-type configuration for the purpose of performingmeasurement of bromate ions according to the present invention.

FIG. 12 Simplified schematic representation of means for measuringfluorescence intensity for the purpose of performing measurement ofbromate ions according to the present invention.

FIG. 13 Simplified flowchart of an apparatus having a batch-typeconfiguration for the purpose of measuring the bromate ions according tothe present invention.

DESCRIPTION OF REFERENCE NUMERALS

-   10 Fluid feed system-   11 Sample supplying means-   12 Pure water supplying means-   13 Standard bromate ion sample supplying means-   14 Chelating agent supplying means-   15 Fluorescent substance supplying means-   16 Acid solution supplying means-   17 a-d Valves-   18 a-e Pumps-   19 Effluent holding means-   20 Constant temperature chamber-   21 Mixing cell-   22 Stirrer-   23 Fluorescence intensity measurement means-   24 Reaction coil-   30 Control means-   120 Excitation light source-   121 a-c Collimator lenses-   122 a-c Slits-   123 a, b Bandpass filters-   124 Beam splitter-   125 a, b Photomultiplier tube-   130 Sample-   131 Chelating agent-   132 Fluorescent substance-   133 Acid solution-   134 Mixing step-   135 Fluorescence intensity measurement

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION

One aspect of a bromate ion measurement method according to the claimsis described below. The present invention is not restricted to theaspect thereof described below.

The measurement of bromate ions in the present invention will bedescribed, with reference made to FIG. 13. First, a sample 130 for whichthe bromate ion concentration is to be measured is prepared. It ispreferable that a chelating agent 131 be added to the sample 130 for thepurpose of masking coexisting metallic ions. The sample is mixed with afluorescent substance 132 that is extinguished by coexistence withbromate ions in the presence of acidity. After mixing, by making the pHof the sample acidic by the addition of an acid solution 133, thefluorescent substance 132 is extinguished with dependency on theconcentration of bromate ions included in the sample. The bromate ionmeasurement method of the present invention makes use of the property ofthe fluorescent substance 132 that it is extinguished by the coexistencewith bromate ions in the presence of acidity, and by measuring thefluorescence intensity after extinguishing using the fluorescenceintensity measuring means, it is possible to determine the bromate ionconcentration included in the sample from the priorly determinedrelationship between fluorescence intensity and bromate ions.

Also, in the present invention it is possible to measure thefluorescence intensity by aging 134 over approximately 2 minutes fromacidifying the sample by the addition of an acid solution 133, and it ispossible to quickly perform the steps from taking the sample through thedetermination of the bromate ion concentration included in the sample.Therefore, according to the bromate ion concentration measurement methodof the present invention, it is possible to quickly measure the bromateion concentration in units of 0.001 mg/L, without the need for complexprocess steps or equipment.

Also, even if there is inclusion of metallic ions in the sample thatrepresent noise in the fluorescence intensity measurement, andparticularly if Fe2+, Fe3+, and Mn2+ are included, by adding thechelating agent 131 to the sample for the purpose of masking themetallic ions before the fluorescent substance mixing, the tolerablelimit of coexisting metallic ions becomes large, and it is possible tomeasure the bromate ion concentration in the same manner, with highsensitivity.

It is sufficient that the fluorescent substance 132 used in the presentinvention be a fluorescent substance having the property of beingextinguished by coexistence with bromate ions in the presence ofacidity, for example, phenothiazine derivatives such as phenothiazine,chlorpromazine, and methyl blue or the like. Of these, trifluoroperazine(TFP) is the most preferable as the fluorescent substance used in thepresent invention.

Trifluoroperazine has phenochiadine in the basic molecular structure,and it has been reported that it is dimerization by oxidation (P.Hanson, R. O. C. Norman, J. Chem. Soc. Perhkin Trans. 2, 164-267(1973)). In trifluoroperazine as well, there is thought to be the sametype of reaction mechanism by oxidation by bromate ions in accordancewith the equations given below, and it is thought that the extinguishingphenomenon occurs in the fluorescence at a particular fluorescencewavelength and excitation wavelength, by trifluoroperazine causing achange in the structure.

The samples that can be measured by the present invention includesedimentation processed water and filtered water in the waterpurification process that contain minute amounts of bromate ions.

An acid solution 133 is used for the purpose of adjusting the sample toacidity in the present invention, and hydrochloric acid is the mostpreferable as the acid solution.

It is sufficient that the chelating agent 131 used in the presentinvention be capable of masking metallic ions coexisting in the sample,and it is preferable that this be ethylene diamine tetraacetate (EDTA).

FIG. 10 shows a simplified schematic drawing of an apparatus having abatch-type configuration. As shown in FIG. 10, a batch-type measurementapparatus for bromate ions according to the present invention is formedby a liquid feed system 10 formed by sample supplying means 11, purewater supplying means 12, standard bromate ion sample supplying means13, chelating agent supplying means 14, fluorescent substance supplyingmeans 15, acid solution supplying means 16, a mixing cell 21, a starter22, an effluent holding means 19, a valve 17, and a valve 18, a constanttemperature chamber 20, a fluorescence intensity measurement means 23,and a control section 30 that controls the fluorescence intensitymeasurement means 23.

It is possible to hold the sample to be measured for bromate ionconcentration in the sample supplying means 11, and it is possible tofeed a prescribed amount of sample to the mixing cell 21 or the reactioncoil 24.

It is possible for the pure water supplying means 12 to store pure waterused as the standard sample (blank) that does not contain bromate ionsfor the purpose of calculating the calibration line, and it is possibleto use it to supply a prescribed amount thereof to the mixing cell 21 orthe reaction coil 24 as appropriate. Also, a prescribed amount of thepure water supplied by the pure water supplying means 12 may also beused for cleaning after sample measurement.

The standard bromate ion sample supplying means 13 can hold a standardsample that does not contain bromate ions for the purpose of calculatingthe calibration line, and can be used to supply a prescribed amount ofthe standard bromate ion sample to the mixing cell 21 or the coil 24 asappropriate.

The chelating agent supplying means 14, the fluorescent substancesupplying means 15, and the acid solution supplying means 16 canrespectively be used to hold chelating agent, a fluorescent substance,and an acid solution, and it is sufficient that a pump supply thechelating agent, the fluorescent substance, and the acid solution to themixing cell 21 or the reaction coil 24. Also, the fluorescent substancesupplying means 15 desirably has a configuration that enables completelight blockage, for the purpose of preventing quenching of thefluorescent substance.

It is sufficient that a mixing cell 21 that is usable in a batch-typeconfiguration be capable of mixing the sample, and the chelating agent,the fluorescent substance, and the acid solution supplied by each of theabove-noted supplying means, and it is preferable that it have a highpermeability, and be very usable under acidic conditions. It is possibleto use a quartz cell, for example, as the mixing cell 21. Also, there isa stirrer 22 installed at the bottom of the mixing cell 21, and thestirrer 2 can mix the sample and the like within the mixing cell 21.

It is sufficient that the stirrer be capable of stirring the sample orthe like within the mixing cell 21, and this can be, for example, amagnetic stirrer or an ultrasonic stirrer or the like, as known in theconventional art. It is preferable that the mixing cell 21 be providedwith a rotor to enable stirring by means of the stirrer 22. A samplethat is stirred and mixed with a chelating agent, a fluorescentsubstance, and an acid solution by the stirrer 22 is measured forfluorescence intensity of the fluorescent substance by the fluorescenceintensity measurement means 23.

The sample after fluorescence intensity measurement is fed as effluentto the effluent holding means 19. It is sufficient that the effluentholding means 19 be capable of temporarily holding effluent from themixing cell 21 after measurement which is to be disposed of.

It is sufficient that the fluorescence intensity measurement means 23 becapable of measuring the intensity of fluorescence emitted by thefluorescent substance by the application of excitation light to thefluorescent substance in the sample.

The constant temperature chamber 20 can control the temperature of themixing cell 21, the stirrer 22, the fluorescence intensity measurementmeans 23, and the reaction coil 24, and can control the temperature ofthe sample for which the fluorescence intensity is to be measured. Therange of temperature controlled by the constant temperature chamber 20is preferably no greater than 25° C. and more preferably 5° C. to 15° C.

The control section 30 can oversee control of the opening and closing ofvalves that control the supply samples and the like from each supplyingmeans, control of the stirring within the mixing cell 21 by the stirrer22, temperature control of the constant temperature chamber 20, andcontrol of the fluorescence intensity measurement means. Also, thecontrol section 30 calculates the measured fluorescence intensity fromthe fluorescence intensity of the standard sample that does not includebromate ions, performs the step of calculating the fluorescenceintensity difference, and uses the calibration line determinedbeforehand between the fluorescence intensity difference and the bromateion concentration to perform the step of calculating the bromate ionconcentration from the calculated fluorescence intensity difference.

According to the above-noted batch-type bromate ion measurementapparatus, the sample for which the bromate ion concentration is to bemeasured is first prepared in the sample supplying means 11. Next, thevalve 17 a and pump 18 a are controlled so as to supply the sample tothe mixing cell 21. When this is done, in the case of supplying purewater or a standard bromate ion sample to the mixing cell 21, bycontrolling each of the pumps 17 b and 17 c, supply is possible to themixing cell 21. Next, the chelating agent is supplied to the mixing cell21 by the chelating agent supplying means 14. After that, thefluorescent substance is supplied to the mixing cell 21 by thefluorescent substance supplying means 15. After supplying thefluorescent substance, the acid solution is supplied to the mixing cell21 by the acid solution supplying means 16. In the mixing cell 21, thestirrer 22 stirs the sample, the chelating agent, the fluorescentsubstance, and the acid solution. When this is done, the temperaturewithin the mixing cell 21 is controlled. After mixing of the sample, thefluorescence intensity measurement means 23 measures the intensity ofthe fluorescence emitted from the fluorescent substance in the sample.After measurement of the fluorescence intensity, in the control section30 b, the fluorescence intensity difference is calculated by subtractingthe measured fluorescence intensity from the fluorescence intensity ofthe standard sample that does not include bromate ions. Next, using thepre-determined calibration line between the fluorescence intensitydifference and the bromate ion concentration, the bromate ionconcentration is calculated from the fluorescence intensity difference.After the fluorescence intensity measurement, the sample is sent aseffluent to a means that receives the sample. The supply of the sampleand the chelating agent can be done by control of the valves 17 a-c andpumps 18 a-d by the controller section 30. In the same manner, theprocessing of the effluent from the mixing cell 21 can be controlled bythe control section 30 controlling the valve 17 d and the pump 18 e.

Next, FIG. 12 shows an aspect of a fluorescence intensity measurementmeans 23 of the present invention. As shown in FIG. 12, the fluorescenceintensity measurement means 23 is formed by an excitation light source120, collimator lenses 121 a-c, slits 122 a-c, bandpass filters (BPFs)123 a, b, a beam splitter 124, photomultiplier tubes (PMTs) 125 a, b,and the mixing cell 21.

It is sufficient that excitation light source 120 be capable of emittinga source of light to strike the fluorescent substance of the sample inthe mixing cell 21 or a flow cell, and this can be a xenon lamp, amercury xenon lamp, or a halogen lamp or the like.

The collimator lens 121 a can collimate the scattered light from theexcitation light source 120 in the direction of the mixed sample. Thecollimator lens 121 b can collimate the wavelength emitted from thefluorescent substance within the mixed sample in the direction of thePMT 123 b for measuring fluorescence. Also, the collimating lens 121 ccan collimate a wavelength that is emitted from the fluorescentsubstance and passes through the BPM 123 b to the measurement positionof the PMT 125 b for measuring the fluorescence. Conventional knownlenses can be used as such collimator lenses.

The slit 122 constricts the light collimated by the collimator lens fromthe excitation light source. As long as this configuration is adopted,it is possible to use a conventional known slit.

The bandpass filter (BPM) 123 a can block a particular wavelength, andsend a particular wavelength to the mixed sample. The BPM 123 b, in thesame manner, can block a particular wavelength and send a particularwavelength only to the PMT 125 b. It is preferable that, as a bandpassfilter, a filter that passes only a wavelength of 300 nm or 480 nm beused, and it is possible for this to be a known conventional type.

It is sufficient that the beam splitter 124 be capable of splitting intotwo the incident light, and this can be a known conventional type.

The photomultiplier tube (PMT) 125 a can measure the temporal variationswith regard to the amount of light from the excitation light source, andit is possible to use this measured value for correction at the time thefluorescence intensity is calculated. Also, the PMT 125 b measures theamount of light at the wavelength emitted from the fluorescent substancewithin the sample. It is possible to use a known conventional type ofPMT.

According to the fluorescence intensity measurement means 23 shown inFIG. 12, scattered light emitted from the excitation light source 120 iscollimated by the collimator lens 121 a, passes through the slit 122 a,and enters the BPM 123 a. The BPM 123 a passes only the wavelength of300 nm, and sends the wavelength of 300 nm to the beam splitter 124. Atthe beam splitter 124 one of the two split wavelengths passes throughthe slit 122 b, and is sent to the PMT 125 a. At the PMT 125 a, in orderto perform correction at the time of measurement of the fluorescenceintensity, the temporal variations in the amount of light from theexcitation light source 120 are measured. The other wavelength thatpasses through the beam splitter 124 enters the mixing cell 21, andexcites the fluorescent substance. The wavelength emitted from theexcited fluorescent substance is collimated by the collimator lens 121 band enters the BPM 123 b. The BPM 123 b blocks wavelengths other than480 nm, and sends the 480-nm wavelength to the slit 122 c. Thewavelength that passes through the slit 122 c is once again collimatedto the position of the PMT 125 b that measures the fluorescenceintensity. The PMT 125 b measures the fluorescence intensity of thewavelength emitted from the fluorescent substance.

FIG. 11 is a simplified schematic drawing of an apparatus having a flowinjection configuration for the purpose performing measurement ofbromate ions according to the present invention. As shown in FIG. 11,the flow injection type measurement apparatus for bromate ions accordingto the present invention is formed by sample supplying means 11, thepure water supplying means 12, the bromate ion standard sample supplyingmeans 13, the chelating agent supplying means 14, the fluorescentsubstance supplying means 15, the acid solution supplying means 16, thepumps 18 a-d, the reaction coil 24, the constant temperature chamber 20,the fluorescent substance intensity measurement means 23, and theeffluent holding means 19.

It is sufficient that the reaction coil 24 that can be used in the flowinjection type configuration have a constitution that enables mixingwhile the sample, the chelating agent, the fluorescent substance, andthe acid solution supplied by the supplying means are flowingcontinuously in the reaction coil 24. The length of the reaction coil 24and the flow amount therein are preferably set appropriately such thatthe sample and the like are sufficiently mixed. The sample that is mixedwithin the reaction coil 24 has its fluorescence intensity measured bythe fluorescence intensity measurement means 23.

According to the above-noted flow injection type bromate ion measurementapparatus, the sample to be measured for bromate ion concentration isprepared in the sample supplying means 11. Next the pump 18 iscontrolled and the sample is supplied to the reaction coil 24. When thisis done, in the case in which pure water or a standard bromate ionsample is supplied to the reaction coil 24, the respective valves (notshown in the drawing) are controlled to perform supply to the reactioncoil 24. Next, in the midway in the pipe that supplies the sample to thereaction coil 24, a chelating agent is supplied by the chelating agentsupplying means 14. After that, in the same manner, midway in the pipethe fluorescent substance is supplied by the fluorescent substancesupplying means 15. After supplying the fluorescent substance, the acidsolution is further supplied to within the reaction cell by the acidsolution supplying means 16. The reaction cell 24 is constituted so asto sufficiently mix the sample, the chelating agent, the fluorescentsubstance, and the chelating agent flowing therewithin, and the reactioncoil 24 is temperature controlled by the constant temperature chamber20. The intensity of the fluorescence emitted by the fluorescentsubstance within the sample that is mixed in the reaction coil 24 ismeasured by the fluorescent substance intensity measurement means 23,and the location measured by the fluorescence intensity measurementmeans 23 has a flow cell configuration so as to enable measurement ofthe sample flowing within the flow cell. After fluorescence intensitymeasurement, the sample is sent as effluent to the effluent holdingmeans 19.

EXAMPLES

Although the present invention is further particularly illustrated belowby embodiments, the present invention is not restricted to theseembodiments.

Example 1

The dependency of trifluoroperazine fluorescence intensity on thebromate ion concentration was measured under acidic conditions.Specifically, after sequentially adding and mixing a 3.2-ml bromate ionsample solution, 0.2 ml of TFP solution, and 0.6 ml of acid solution ina sample tube, the fluorescence was measured after 2 minutes (with anexcitation wavelength of 300 nm, and a fluorescence wavelength of 485nm) using a fluorescence spectrophotometer (product name: F4500, made byHitachi). In the bromate ion sample solution, the proportions of bromateion concentrations were, respectively, a) blank (no bromate ioncontent), b) 7.5 μg/L, and c) 15 μg/L. FIG. 2 shows the fluorescencespectrum of trifluoroperazine with respect to samples with variousbromate ion concentrations. From these results, it was seen that aquenching phenomenon occurred due to the bromate ion. Also, it wasdetermined that, as the bromate ion concentration increased, thequenching of the fluorescence became greater.

Example 2

An investigation was made of the trifluoroperazine concentration used inthe measurement method of the present invention. Using the same type ofstep as in Example 1, the measurement method for bromate ions wasperformed. An acid solution and hydrochloric acid were used, with thehydrochloric acid set to 1.0 M. Using bromate ion sample solutions, oneblank and one that was 11 μg/L, the measurement was performed as the TFPconcentration was varied. The fluorescence intensity differences betweenthe solution containing bromate ions and the blank corresponding to theTFP concentrations were obtained. The results regarding the influence ofthe concentration of the added TFP and the thus-obtained fluorescenceintensity differences (the differences between the fluorescenceintensity of the blank sample and the fluorescence intensity of thesample having a bromate ion concentration of 11 μg/L) are shown in FIG.3. The difference in fluorescence intensity between the blank and thesample containing bromate ions increased up to a trifluoroperazineconcentration of 7.35×10⁻⁶ M, after which it was constant. From theseresults, it is thought that bromate ions completely react at atrifluoroperazine concentration of at least 7.35×10⁻⁶ M. In thefollowing embodiments, the concentration of trifluoroperazine was made7.35×10⁻⁶ M.

Example 3

An investigation was performed of the acid used in the bromate ionmeasurement method of the present invention. Using the same type of stepas in Example 1, the measurement method for bromate ions was performed.When this was done, a comparison was performed by using hydrochloricacid, nitric acid, and sulfuric acid in the acid solution. GivenEmbodiment 2, the concentration of trifluoroperazine was made 7.35×10⁻⁶M, and the bromate ion concentration was varied from 0 to 15 μg/L. Inthe case of using hydrochloric acid in the acid solution, addition wasdone to make the hydrochloric acid concentration 0.9 M ([H⁺]_(T)=0.9 Mand [Cl⁻]_(T)=0.9 M), and the results are shown in FIG. 4. In the caseof using nitric acid in the acid solution, addition was done to make thenitric acid concentration 0.9 M ([M⁺]_(T)=0.9 M and [NO₃ ⁻]_(T)=0.9 M),and the results are shown in FIG. 5. In the case of using sulfuric acidin the acid solution, addition was done to make the sulfuric acidconcentration 0.45 M ([H⁺]_(T)=0.9 M and [SO₄ ²⁻]_(T)=0.45 M, and theresults are shown in FIG, 6.

In the case of using hydrochloric acid in the acid solution, the resultwas a quantitative decrease in the fluorescence intensity with respectto the bromate ion concentration. In the case of using nitric acid, thefluorescence intensity was approximately 1/444 compared with the case ofusing hydrochloric acid. In the case of using sulfuric acid, althoughthe same level of fluorescence intensity was obtained as with the caseof using hydrochloric acid, there was no quantitative decrease in thefluorescence intensity with respect to the bromate ion concentration.From these results, therefore, it is possible to quantitativelydetermine the bromate ions when using hydrochloric acid as the acidsolution.

Example 4

An investigation was performed on the influence of varying thehydrochloric acid concentration when hydrochloric acid is used in theacid solution. Using the same type of step as in Embodiment 1, themeasurement method for bromate ions was performed. The TFP concentrationwas set to 7.35×10⁻⁶ M, the bromate ion concentration was set to 11μg/L, and the hydrochloric acid concentration was varied from 0.25 to1.5 M. FIG. 7 shows the relationship between the hydrochloric acidconcentration and the fluorescence intensity. Because the fluorescenceintensity difference between blank and the sample was maximum at ahydrochloric acid concentration of 1.0 M, the hydrochloric acidconcentration was set to 1.0 M. It is thought that the decrease in thefluorescence intensity below 1.0 M is due to insufficient acidity forthe quenching reaction to occur, and it is thought that the decrease inthe fluorescence intensity at about 1.0 M is due to the prevention ofdimers as the reaction of emitting protons proceeds to the right side inthe reaction mechanism.

Example 5

An investigation was performed on the relationship of the reaction timeand various bromate ion concentrations to the fluorescence intensity.Using the same type of step as in Example 1, the measurement method forbromate ions was performed. The TFP concentration was set to 7.35×10⁻⁶M, hydrochloric acid was used in the acid solution, and the hydrochloricacid concentration was set to 1.0 M. The bromate ion concentrations usedwere blank, 7.5 μg/L, and 15 μg/L. The reaction time from the adding ofthe hydrochloric acid to the sample to which the TFP solution had beenadded was varied and the respective fluorescence intensities at 25° C.were measured. FIG. 8 shows the relationship of the reaction time andbromate ion concentration to the fluorescence intensity. Because nochange was observed after the elapse of 2 minutes of reaction time inall cases of the bromate ion concentrations of 7.5 μg/L, 15 μg/L, andblank, the reaction time was set to approximately 2 minutes. In thedrawing, the reaction times are indicated with the addition of the acidsolution taken as being 0 seconds.

Example 6

An investigation was performed on the dependency of fluorescenceintensity on bromate ion concentration. Using the same type of step asin Example 1, the measurement method for bromate ions was performed. TheTFP concentration was set to 7.35×10⁻⁶ M, hydrochloric acid was used asthe acid solution, and the hydrochloric acid concentration was set to1.0 M. The bromate ion concentration in the sample was varied and thefluorescence intensity difference was measured to obtain a bromate ioncalibration line. FIG. 9 shows the bromate ion concentration calibrationline. The relationship between bromate ion concentration in the sampleand fluorescence intensity difference obtained from this calibrationline was y=26.42x (where y is the fluorescence intensity difference andx is the bromate ion concentration in μg/L), the correlation coefficientbeing 0.997. At a bromate ion concentration of 7.5 μg/L, the relativestandard deviation with 5 measurements was 2.71%, and the detectionlimit (3σ) was 0.58 μg/L.

Example 7

An investigation was performed on the influence of coexisting substanceson the fluorescence intensity difference with a bromate ion blank and abromate ion concentration of 7.5 μg/L (6.0×10⁻⁸ M), and the results areshown in Table 1. The tolerable concentration limit of a coexistingsubstance, taken as the concentration that results in an error within±5% in the above-noted fluorescence intensity difference, was comparedby molar ratios with the bromate ion concentration. As a result, atolerable limit for Al⁺³, Ca²⁺, K⁺, Na⁺, Ni²⁺, Mg²⁺, Cl⁻, NO₃ ⁻, and SO₄²⁻ was ×1000, and for Zn²⁺, IO₃ ⁻, IO₄ ⁻, and EDTA was ×100. Also,although the tolerable limit was a low value of ×1 for Fe²⁺Fe³⁺, andMn²⁺, by using EDTA as a masking agent, it was possible to allow thetolerable limit to be ×10 for Fe²⁺, Fe³⁺, and Mn²⁺.

TABLE 1

*Masked by [EDTA]_(T) = 6.0 ×10⁻⁷ M [BrO₃ ⁻]_(T) = 6.0 ×10⁻⁸ M (7.5μg/L) [TFP]_(T) = 7.35 × 10⁻⁶ M, [HCl]_(T) = 1.0 M

Embodiment 8

As an application of the present method, a quantitative determinationwas made of the bromate ions included in the commercially availableCrystal Geyser (made by CG Roxane), using the standard addition method,the result being shown in Table 2. At a bromate ion concentration of 7.5μg/L, the relative standard deviation was 3.02%. Also, good results wereobtained for the potassium bromide recovery rate, which was 96% at 7.5μg/L and 103% at 15 μg/L.

TABLE 2 Amount Detected Recovery added (μg/L) value (μg/L) rate (%)Blank N.D. —  7.5  7.2  96 15.0 15.5 103

A comparison of the present method with other methods is shown in Table3. The present fluorescence intensity method, compared with the ionchromatography post-column method¹ currently adopted as a method oftesting for bromate ions (“Drinking Water Testing Methods” 2001 Edition,Expanded Edition, p. 16 (2006), (Japan Water Works Association)), theabsorption spectrographic method using a 1-cm cell²⁾ (Non-PatentReference 1) and the absorption spectrographic method using a 10-cmcell²⁾ (Non-Patent Reference 2), is simpler than the former, and withrespect to the latter has a 10-fold improvement in sensitivity and doesnot require a special cell and analytical equipment, making it moregenerally usable.

TABLE 3 Quantitative Detection determination limit (3σ) Method Cell (cm)range (μg/L) (μg/L) Fluorescence intensity 1 0.8-15 0.58(trifluoroperazine) Absorption spectrography 10    1-700 0.67(trifluoroperazine) Absorption spectrography 1   50-150 10 (triiodide)Ion chromatography post — 0.5-50 0.19 column absorption spectrography(tribromide)

1. A method for measuring bromate ions in a sample, comprising the stepsof: mixing a fluorescent substance with the sample, the fluorescentsubstance being quenched by coexistence with bromate ions under acidicconditions; measuring a florescence intensity after quenching of thefluorescent substance; subtracting the measured fluorescence intensityfrom a fluorescence intensity of a standard sample that does not containbromate ions to calculate a fluorescence intensity difference; and astep of using a pre-determined calibration line between the fluorescenceintensity difference and the bromate ion concentration to calculate thebromate ion concentration from the calculated fluorescence intensitydifference.
 2. The method according to claim 1, wherein the methodfurther comprises a step of adding a chelating agent to the samplebefore the step of mixing the fluorescent substance and the sample. 3.The method according to claim 1, wherein the fluorescent substance istrifluoroperazine.
 4. The method according to claim 2, wherein thechelating agent is ethylene diamine tetraacetate.
 5. The methodaccording to claim 2, wherein the fluorescent substance istrifluoroperazine.
 6. The method according to claim 5, wherein thechelating agent is ethylene diamine tetraacetate.
 7. An apparatus formeasuring the bromate ions in a sample, comprising: means for mixing afluorescent substance with a sample, the fluorescent substance to bequenched by coexistence with bromate ions under oxidizing conditions;means for measuring a fluorescence intensity after quenching of thefluorescent substance; means for subtracting the measured fluorescenceintensity from a fluorescence intensity of a standard sample that doesnot contain bromate ions to calculate a fluorescence intensitydifference; and means for using a pre-determined calibration linebetween the fluorescence intensity difference and the bromate ionconcentration to calculate the bromate ion concentration from thecalculated fluorescence intensity difference.
 8. The apparatus accordingto claim 7, wherein the apparatus is constituted so as to measure theadmixture of the sample and the fluorescent substance that istemporarily held in the mixing means with the fluorescence intensitymeasuring means.
 9. The apparatus according to claim 7, wherein theapparatus is constituted so as to measure with the fluorescenceintensity measuring means the admixture of the sample and thefluorescent substance that flows continuously in the mixing means.